1. Field of the Invention The present invention is directed to tubing, piping, conduit, any roll formed closed geometric shapes and the like. More particularly, the present invention relates to coating the interior wall or surface of pipe used in fire sprinkler or non-potable or potable water transfer systems where the coating has a low friction composition to provide low flow resistance over the life of the system.
2. Discussion of Related Art
The art of forming and coating tubes, pipes and conduits (hereinafter referred to generally as “pipe” and/or “pipes”) is well-established. To form a pipe, strip steel in the form of coils is supplied from a pay-out reel in a pipe forming mill or line. The width of the strip steel is proportional to the diameter of the pipe to be formed and is supplied to one or more tube forming rollers in a tube forming station to bring the longitudinal edges of the strip steel together. The edges are then welded together to form a pipe having a generally circular or closed geometric shape such as square or rectangular cross-section. After the welding process, an alkali solution may be applied to the pipe for cleaning purposes. The pipe may be subsequently heated and treated (e.g. galvanized) for corrosion protection. The pipe is typically heated before galvanizing to ensure that the temperature of the hot dip zinc is maintained at the desired temperature. Otherwise, providing a “cold” pipe to the hot dip material would decrease the temperature of the zinc during the coating process. The pipe is then cut to a desired length. The various steps in this process are aligned along the central axis of the pipe and are continuous within a mill to produce pipe at relatively high rates of speed.
As noted above, galvanizing is a process where the formed pipe is exposed to a zinc or molten metallic coating on the outside wall of the pipe. Galvanizing or metallic coating takes advantage of the protective properties of zinc or applied metal which is more resistant to corrosion than the underlying steel pipe. Advances in pipe manufacturing and galvanizing have resulted in the production of continuous pipes at rapid speeds on the order of one thousand (1000) feet per minute. Application dwell times of zinc during galvanizing have been reduced to tenths of seconds and contact zones of the pipe upon which the zinc is applied have similarly been reduced to inches. Preferred methods for coating pipes are described in U.S. Pat. Nos. 6,063,452 and 6,197,394, herein incorporated by reference. However, these processes are related to coating on the outside walls of the pipe not the inside wall of the centrally disposed pathway.
U.S. Pat. No. 5,718,027 (“the '027 patent”) discloses an apparatus for the interior painting of tubing during continuous formation of the pipe which is assigned to the assignee of the present invention the contents of which are herein incorporated by reference. The '027 patent teaches the use of a spraying means which is introduced into the pipe upstream of the welding station while providing the spraying means downstream of the processing stations for forming the pipe.
Fire protection systems (e.g. sprinkler systems) employ these types of coated pipes for installation within buildings or structures to provide fire suppression liquids (e.g. water) or suppressants throughout the premises. These sprinkler systems are engineered and designed to provide the requisite amount of fire suppression fluid typically water to the desired area. However, the pipes used in these systems are susceptible to corrosion of the base metal which degrade over time. For example, the inside surface of the uncoated black pipe deteriorates over time resulting in decreased hydraulic efficiency. This is due, at least in part, to the theoretical eventual roughening of the pipe's internal diameter (I.D.) surface from oxidation (rust) or microbiological induced corrosion (M.I.C.) over the life of the pipes and systems. MIC is a corrosion process based on microorganisms (aerobes and anaerobes) and is a major cause of tuberculation, pitting and pipe failure in fire sprinkler systems employing carbon steel, copper, and galvanized pipe. To account for these factors, sprinkler systems are designed using the Hazen-Williams equation which factors in the roughness coefficient or C-Factor of the ID of the sprinkler pipe based on this pipe degradation over time. Methods used by manufacturers of fire sprinkler piping to overcome these degradation problems within the sprinkler pipe have included the use of plastic lined piping with a separate plastic insert sleeve within the interior pathway of the pipe as well as offline diffusion coatings. However, such plastic lined piping has poor heat resistance to fire combustion temperatures, causes changes in the dimension of the I.D. of the piping, has a high potential for delamination, and requires special tooling and fittings for pipe fabrication not routinely found in the fire protection industry. Another method used for pulling fiber optic cables through conduit is to provide a lubricous material impregnated in an inner duct of the conduit. However, this method does not address the degradation requirements associated with water or other fire suppressants over the life of a fire protection system. Thus, there is a need to provide a pipe that can withstand ID degradation and provide an improved C-Factor over the life of a fire sprinkler system